Without repeating much of what has been said, when using the M9 at low ISO, I generally follow the logic and protocol of Chuck & John. When the ISO is raised beyond 1250, Jaap's suggestions are warranted and good advice, in my opinion.
At low ISO, I preserve most highlights and avoid blowing them out, because its often difficult (and sometimes impossible to recover what's essentually lost. At low ISO's, especially baseline (160), noise levels are extremely low and so it's possible to open up the shadows with much deleterious effect. As the ISO range is increased due to low light, the histogram becomes more important to watch and although I try to expose more for shadow detail, to avoid excessive noise. I will though watch for exposing the highlights (those specifically below spectral levels), in order that as much highlight detail is preserved, but not at the expense of losing shadow detail due to rising noise levels A balanced approach is carefully followed for both ends of the histogram in this case.
Dave (D&A)
At low ISO, I preserve most highlights and avoid blowing them out, because its often difficult (and sometimes impossible to recover what's essentually lost. At low ISO's, especially baseline (160), noise levels are extremely low and so it's possible to open up the shadows with much deleterious effect. As the ISO range is increased due to low light, the histogram becomes more important to watch and although I try to expose more for shadow detail, to avoid excessive noise. I will though watch for exposing the highlights (those specifically below spectral levels), in order that as much highlight detail is preserved, but not at the expense of losing shadow detail due to rising noise levels A balanced approach is carefully followed for both ends of the histogram in this case.
Dave (D&A)